In testing and mounting semiconductor devices, it is necessary that the leads of the device be correctly positioned and that the ends of the leads lie in a common plane. This is particularly true for surface-mount devices. The leads of the semiconductor device may be bent sideways, out, in or down, thereby moving the end of the pin from a plane common with the ends of the other pins. In some instances, one or more pins may have a greater height than the others.
Existing planarity inspection equipment is either not cost-effective or performs the inspection "off-line" as in a quality control operation. The hardware required for off-line inspection is inexpensive; however, the inspection is done manually, lead by lead, making 100% inspection time-consuming, as well as labor cost prohibitive. Automatic equipment which can be used for on-line inspection is actually stand-alone equipment integrated with the other processing equipment.
In order to inspect for coplanarity of the leads of a surface-mount device using machine vision, the leads must be located, and the machine vision image converted to scale units such a millimeters or mils using a scale factor. The data has to be converted from multiple two-dimension coordinate frames to a three-dimensional coordinate frame using a plane for reference. Present systems using the above method for determining planarity have to be calibrated prior to each series of devices to be tested, and pixel jitter or motion, after calibration, is not detected during cap of the picture and may cause errors.